Method for repairing high temperature articles

ABSTRACT

A method for repairing an article comprises providing an article, providing a repair material, and joining said repair material to said article. The repair material comprises, in atom percent, at least about 50% rhodium; up to about 49% of a first material, said first material comprising at least one of palladium, platinum, iridium, and combinations thereof; from about 1% to about 15% of a second material, said second material comprising at least one of tungsten, rhenium, and combinations thereof; and up to about 10% of a third material, said third material comprising at least one of ruthenium, chromium, and combinations thereof. The repair material comprises an A1-structured phase at temperatures greater than about 1000° C., in an amount of at least about 90% by volume.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 10/747,712 filed on Dec. 23, 2003, which is hereby incorporatedby reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to materials designed to withstand hightemperatures. More particularly, this invention relates toheat-resistant alloys for high-temperature applications, such as, forinstance, gas turbine engine components of aircraft engines and powergeneration equipment. The present invention further relates to methodsfor repairing articles for high temperature applications.

There is a continuing demand in many industries, notably in the aircraftengine and power generation industries where efficiency directly relatesto equipment operating temperature, for alloys that exhibit sufficientlevels of strength and oxidation resistance at increasingly highertemperatures. Gas turbine airfoils on such components as vanes andblades are usually made of materials known in the art as “superalloys.”The term “superalloy” is usually intended to embrace iron-, cobalt-, ornickel-based alloys, which include one or more additional elements toenhance high temperature performance, including such non-limitingexamples as aluminum, tungsten, molybdenum, titanium, and iron. The term“based” as used in, for example, “nickel-based superalloy” is widelyaccepted in the art to mean that the element upon which the alloy is“based” is the single largest elemental component by atom fraction inthe alloy composition. Generally recognized to have service capabilitieslimited to a temperature of about 1200° C., conventional superalloysused in gas turbine airfoils often operate at the upper limits of theirpractical service temperature range. In typical jet engines, forexample, bulk average airfoil temperatures range from about 900° C. toabout 1100° C., while airfoil leading and trailing edge and tiptemperatures can reach about 1150° C. or more. At such elevatedtemperatures, the oxidation process consumes conventional superalloyparts, forming a weak, brittle metal oxide that is prone to chip orspall away from the part.

Erosion and oxidation of material at the edges of airfoils lead todegradation of turbine efficiency. As airfoils are worn away, gapsbetween components become excessively wide, allowing gas to leak throughthe turbine stages without the flow of the gas being converted intomechanical energy. When efficiency drops below specified levels, theturbine must be removed from service for overhaul and refurbishment. Asignificant portion of this refurbishment process is directed at therepair of the airfoil leading and trailing edges and tips. For example,damaged material is removed and then new material built onto the bladeby any of several methods, such as, for example, welding with fillermaterial, welding or brazing new sections onto the existing blade, or byplasma spraying or laser deposition of metal powders onto the blade. Theperformance of alloys commonly used for repair is comparable or inferiorto that of the material of the original component, depending upon themicrostructure of the repaired material, its defect density due toprocessing, and its chemistry. Furthermore, in current practice, theoriginal edge material is made of the same material as the rest of theoriginal blade, often a superalloy based on nickel or cobalt. Becausethis material was selected to balance the design requirements of theentire blade, it is generally not optimized to meet the special localrequirements demanded by conditions at the airfoil leading or trailingedges. However, maximum temperatures, such as those present at airfoiltips and edges, are expected in future applications to be over about1300° C., at which point many conventional superalloys begin to melt.Clearly, new materials for repair and manufacture must be developed toimprove the performance of repaired components and to exploit efficiencyenhancements available to new components designed to operate at higherturbine operating temperatures.

BRIEF DESCRIPTION

Embodiments of the present invention address these and other needs. Oneembodiment is an alloy comprising, in atom percent, at least about 50%rhodium, up to about 49% of a first material, from about 1% to about 15%of a second material, and up to about 10% of a third material. The firstmaterial comprises at least one of palladium, platinum, iridium, andcombinations thereof. The second material comprises at least one oftungsten, rhenium, and combinations thereof. The third materialcomprises at least one of ruthenium, chromium, and combinations thereof.The alloy comprises an A1-structured phase at temperatures greater thanabout 1000° C., in an amount of at least about 90% by volume.

Another embodiment is an article for use in a high temperature,oxidative environment. The article comprises the alloy described above.

A further embodiment is a method for making an article. The methodcomprises providing the alloy described above.

Another embodiment is a method for repairing an article. The methodcomprises providing an article, providing a repair material thatcomprises the alloy described above, and joining the repair material tothe article.

DETAILED DESCRIPTION

The description herein employs examples taken from the gas turbineindustry, particularly the portions of the gas turbine industryconcerned with the design, manufacture, operation, and repair ofaircraft engines and power generation turbines. However, the scope ofthe invention is not limited to only these specific industries, as theembodiments of the present invention are applicable to many and variousapplications that require materials resistant to high temperature andaggressive environments.

The alloy of the present invention balances a number of competingmaterial requirements, including, for example, strength, ductility, andoxidation resistance. The composition ranges developed for this alloyhave been selected based on the need to achieve sufficient strength towithstand the stresses associated with many industrial machinecomponents, while maintaining sufficient ductility to allow the materialto be formed into complex shapes. All of this must be done whilepreserving very high resistance to oxidation.

In accordance with one embodiment of the present invention, the alloycomprises, in atom percent, at least about 50% rhodium and up to about49% of a first material, where the first material comprises at least oneof palladium, platinum, iridium, and combinations thereof. Theseplatinum-group metals are all highly resistant to most forms ofenvironmental attack and provide the alloy of the present invention withextraordinary oxidation resistance at high temperatures. The elementscomprising the first material have A1 crystal structures, as doesrhodium, and at temperatures above about 1000° C. each of these elementsdissolves in rhodium to form a single-phase solid solution having thissame crystal structure. This A1-structured phase provides a desirablecombination of properties. Having a high amount of A1-structuredelements in the alloy promotes the formation and stability of thedesirable single-phase microstructure. Accordingly, in certainembodiments, a sum of the atom percentage of rhodium in the alloy plusthe atom percentage of the first material in the alloy is at least about75 atom percent, and in particular embodiments this sum is at leastabout 85 atom percent. In all cases, the alloy of the present inventioncomprises, at temperatures greater than about 1000° C., at least about90% by volume of the A1-structured phase.

The strength of the alloy is enhanced by additions of other materials.The alloy further comprises from about 1% to about 15% of a secondmaterial comprising at least one of tungsten, rhenium, and combinationsthereof. Moreover, the alloy comprises up to about 10% of a thirdmaterial comprising at least one of ruthenium, chromium, andcombinations thereof. These additions serve to strengthen the alloy viaa solid solution strengthening mechanism, but the amounts added to thealloy are limited by concerns about maintaining oxidation resistance andductility. The amounts of second and third materials added to the alloyare broadly governed by the respective solubilities of the constituentelements in the A1-structured phase, to avoid precipitation ofdeleterious amounts of secondary phases. Moreover, the allowed amountsare further restricted in certain embodiments where oxidation resistanceis a key concern. For example, in particular embodiments the secondmaterial is present in an amount from about 1 atom percent to about 6atom percent; and the third material is present in an amount up to about8 atom percent. In these embodiments, the composition of the thirdmaterial is controlled within the above constraint such that rutheniumis present in an amount up to about 4 atom percent and chromium ispresent in an amount up to about 6 atom percent.

In certain embodiments, a fourth material is added to the alloy toprovide even further strengthening. The fourth material comprises atleast one element that not only provides a certain degree of solidsolution strengthening when the element itself is dissolved in theA1-structured phase, but also forms a highly stable oxide. Such elementsinclude zirconium, yttrium, hafnium, tantalum, aluminum, titanium,scandium, elements of the lanthanide series, and elements of theactinide series. The alloy, in these embodiments, comprises up to about3 atom percent of the fourth material, and in certain embodiments, thefourth material is present in an amount from about 0.1 atom % to about 2atom %. In some embodiments, the fourth material is present in the alloyin the form of a plurality of oxide particles dispersed throughout thealloy, wherein the oxide particles comprise an oxide of the fourthmaterial. The dispersion of fine oxide particles provides aprecipitation strengthening effect to the alloy. Typically, the oxideparticles used to effect strengthening in metallic materials have aparticle size in the range from about 0.1 micrometer to about 10micrometers. This dispersion may be formed in situ by adding the fourthmaterial in metallic form to the alloy and then exposing the alloy to aheat treatment in an oxidizing environment, a process that is widelyknown in the art and an example of which is described in U.S. Pat. No.3,640,705 to Selman et al. Alternatively, at least a portion of thefourth material in oxide form may be directly added to the alloy andmechanically dispersed, in the manner common in the art of mechanicallyalloyed materials. In either case, at least a portion of the fourthmaterial, in some embodiments, is present as a solute dissolved in saidA1 structured phase.

In order to take full advantage of the compositional effects describedabove, embodiments of the present invention further include an alloycomprising, in atom percent, at least about 50% rhodium, and up to about49% of a first material, the first material comprising at least one ofpalladium, platinum, iridium, and combinations thereof. A sum of theamount of rhodium in the alloy plus the amount of the first material inthe alloy is at least about 85 atom percent. The alloy further comprisesfrom about 1% to about 6% of a second material, the second materialcomprising at least one of tungsten, rhenium, and combinations thereof;and up to about 8% of a third material, the third material comprising atleast one of ruthenium, chromium, and combinations thereof. Theruthenium is present in an amount up to about 4 atom percent and thechromium is present in an amount up to about 6 atom percent.Furthermore, the alloy comprises up to about 2% of a fourth material,the fourth material comprising at least one of zirconium, yttrium,hafnium, tantalum, aluminum, titanium, scandium, elements of thelanthanide series, elements of the actinide series, and combinations ofany of the foregoing. The alloy comprises an A1-structured phase attemperatures greater than about 1000° C., in an amount of at least about90% by volume.

Alloys set forth herein as embodiments of the present invention aresuitable for production using any of the various known methods of metalproduction and forming. Conventional casting, powder metallurgicalprocessing, directional solidification, and single-crystalsolidification are non-limiting examples of methods suitable for formingingots of these alloys. Thermal and thermo-mechanical processingtechniques common in the art for the formation of other alloys,including, for instance, forging and heat treating, are suitable for usein manufacturing and strengthening the alloys of the present invention.

Another embodiment is an article for use in a high temperature,oxidative environment. The article comprises the alloy described above.The article may be one that has been repaired, or it may be a newlymanufactured article. In some embodiments, the article comprises acomponent of a gas turbine engine, such as, for example, a turbineblade, vane, or a combustor component. Up to the entire component maycomprise the alloy of the present invention. Furthermore, the alloy ofthe present invention may be suitably disposed anywhere on thecomponent, including, in certain embodiments, at one or more regions ofthe component that are particularly prone to experience high localtemperatures, such as, for example, leading and trailing edges of bladesand vanes, and blade tips. In certain embodiments, the article comprisesa coating disposed on a substrate, and the coating comprises the alloy.Suitable methods for disposing the coating include, for example, thermalspraying, plasma spraying, HVOF spraying, and laser deposition. Havingonly particular sections (i.e., those sections known to experience themost aggressive stress-temperature combinations) of the airfoil comprisethe alloy of the present invention minimizes certain drawbacks of alloyscomprising significant amounts of platinum group metals such as, forexample, platinum, rhodium, and palladium, including their high cost andhigh density in comparison to conventional airfoil materials. Thesedrawbacks have a reduced effect on the overall component because thecomparatively expensive and dense alloy (relative to conventionalsuperalloys) comprises only a fraction of the overall surface area ofthe component. The properties of the component are thus “tailored” tothe expected localized environments, reducing the need for compromiseduring the design process and increasing the expected operatinglifetimes for new and repaired components.

Further embodiments of the present invention include methods for makingthe article described above, and methods for repairing such an article.The method for making the article comprises providing the alloydescribed above. In the method for repairing an article, an article isprovided. The article, in certain embodiments, comprises a component ofa gas turbine engine, including, for example, a blade, a vane, or acombustion component. A repair material is provided, and this repairmaterial comprises the alloy described herein. This repair material isjoined to the article. In some embodiments, joining is accomplished, atleast in part, by disposing a coating comprising the repair materialonto the article being repaired. In other embodiments, the repairmaterial is joined to the substrate by one or more conventional joiningprocesses, including, for example, welding, brazing, or diffusionbonding. Regardless of whether the repair material is in the form of acoating or a solid section, it may be disposed at any section of thearticle deemed to require the performance characteristics of the repairmaterial. These sections include, for example, the leading and trailingedges of airfoils, and blade tips.

While various embodiments are described herein, it will be appreciatedfrom the specification that various combinations of elements,variations, equivalents, or improvements therein may be made by thoseskilled in the art, and are still within the scope of the invention asdefined in the appended claims.

1. A method for repairing an article, said method comprising: providingan article; providing a repair material, said repair material consistingof, in atomic percent: at least about 50 atomic percent rhodium; up toabout 49 atomic percent of a first material, said first materialconsisting of at least one of palladium, platinum, iridium, andcombinations thereof; from about 1 to about 15 atomic percent of asecond material, said second material consisting of at least one oftungsten, rhenium, and combinations thereof; and up to about 10 atomicpercent of a third material, said third material consisting of at leastone of ruthenium, chromium, and combinations thereof; from about 0.1 toabout 2 atomic percent of a fourth material, said fourth materialconsisting of at least one of zirconium, yttrium, hafnium, tantalum,aluminum, titanium, scandium, elements of the lanthanide series,elements of the actinide series, and combinations thereof; wherein saidrepair material has an A1-structured phase at temperatures greater thanabout 1000° C., in an amount of at least about 90% by volume; andjoining said repair material to said article.
 2. The method of claim 1,wherein a sum of the amount of rhodium in the repair material plus theamount of said first material in the repair material is at least about75 atomic percent.
 3. The method of claim 1, wherein joining comprisesat least one of welding, brazing, and diffusion bonding.
 4. The methodof claim 1, wherein joining comprises disposing a coating onto saidarticle, said coating comprising said repair material.
 5. The method ofclaim 4, wherein disposing said coating comprises disposing said coatingby at least one process selected from the group consisting of thermalspraying, plasma spraying, HVOF spraying, and laser deposition.
 6. Themethod of claim 1, wherein said article comprises a component of a gasturbine engine selected from the group consisting of a blade, a vane,and a combustion component.
 7. The method of claim 6, wherein joiningcomprises disposing said repair material on at least one componentsection selected from the group consisting of a leading edge, a trailingedge, and a blade tip.
 8. A method for repairing a gas turbine enginecomponent, said method comprising: providing at least one gas turbineengine component selected from the group consisting of a blade, a vane,and a combustion component; providing a repair material, said repairmaterial consisting of, in atomic percent: at least about 50 atomicpercent rhodium; up to about 49 atomic percent of a first material, saidfirst material consisting of at least one of palladium, platinum,iridium, and combinations thereof; from about 1 to about 6 atomicpercent of a second material, said second material consisting of atleast one of tungsten, rhenium, and combinations thereof; and up toabout 8 atomic percent of a third material, said third materialconsisting of at least one of ruthenium, chromium, and combinationsthereof, wherein said ruthenium is present in an amount up to about 4atom percent and said chromium is present in an amount up to about 6atom percent; and from about 0.1 to about 2 atomic percent of a fourthmaterial, said fourth material consisting of at least one of zirconium,yttrium, hafnium, tantalum, aluminum, titanium, scandium, elements ofthe lanthanide series, elements of the actinide series, and combinationsof any of the foregoing; wherein said repair material has anA1-structured phase at temperatures greater than about 1000° C., in anamount of at least about 90% by volume, and wherein a sum of the amountof rhodium in said repair material plus the amount of said firstmaterial in said repair material is at least about 85 atom percent; andjoining said repair material to said component by disposing said repairmaterial at least one component section selected from the groupconsisting of a leading edge, a trailing edge, and a blade tip.